Examples of composite materials for covering electronic parts include epoxy resin matrices mixed with silica (silicon dioxide). Silica is incorporated because the use of an epoxy resin alone as an exterior covering material results in an increased cost of the electronic components and an exterior covering of insufficient mechanical strength, since epoxy resins are brittle if used alone.
From the standpoint of obtaining enhanced mechanical strength, silica must be uniformly dispersed in the resin matrix. This kind of composite materials for use as an exterior covering of electronic components are therefore prepared by, for example, stirring silica and the resin by means of an appropriate stirring machine, so as to attain uniform dispersion of silica in the resin matrix. Further, it is necessary to evaluate the degree of dispersion of silica in the composite material as a final product.
Representative examples of the methods now available for evaluating the degree of dispersion include:
(1) A liquid composite material is poured into a container having a small-diameter nozzle at the bottom. The composite material drips from the nozzle and forms a thread due to its viscosity. The higher the degree of the silica, the longer the thread. The degree of dispersion can thus be evaluated by visual estimation of the length of the thread; and PA1 (2) A composite material is solidified once, and a solid sample is cut. The cut area is visually observed under a microscope, etc. to obtain a value of the dispersed particles per unit area or the number of the dispersed particles per unit area. The results are used to create histogram, and the degree of dispersion is evaluated from the shape of the histogram. PA1 forming a block sample of the composite material; PA1 dividing the block sample into a plurality of unit volume pieces; PA1 incinerating each of the unit volume pieces in an oxidative atmosphere; PA1 quantitatively determining the ash content of each of the unit volume pieces; and PA1 calculating the scatter of the inorganic material content within the plurality of unit volume pieces.
Method (1) has a problem in that quantitative determination is impossible. The evaluation according to either method is not absolute but relative. The evaluation methods (1) and (2) assume subjectiveness. In particular, method (2) fails to make an evaluation throughout the whole material.